The FBI and NSA monitored the emails of five prominent Muslim Americans, including activists, academics and a political candidate, according to documents leaked by Edward Snowden.

The report on the Intercept, an online news website run by journalist Glenn Greenwald, said the surveillance was approved by a secret intelligence court under procedures intended to locate spies and terrorist suspects.

The White House has expressed dismay at the Intercept's report that the US intelligence services also used a racial slur to refer to Muslim-American surveillance targets.

National security spokeswoman Caitlin Hayden said on Wednesday: "Upon learning of this matter, the White House immediately requested that the Director of National Intelligence undertake an assessment of Intelligence Community policies, training standards or directives that promote diversity and tolerance."

Snowden has applied to extend his asylum in Russia

She said "the use of racial or ethnic stereotypes, slurs, or other similar language" was unacceptable.

The five Muslim-Americans targeted were:

:: Faisal Gill, a long-time Republican Party operative and former political candidate

:: Asim Ghafoor, a lawyer who has represented clients in terrorism-related cases

:: Hooshang Amirahmadi, an Iranian-American professor at New Jersey's Rutgers University

:: Agha Saeed, a civil liberties activist and former professor at California State University

:: Nihad Awad, the executive director of the Council on American-Islamic Relations

Glenn Greenwald has been the conduit for much of Snowden's material

Mr Gill told the Intercept of his shock at the report.

The former Republican candidate for the Virginia House of Delegates said: "I've done everything in my life to be patriotic.

"I served in the Navy, served in the government, was active in my community. I've done everything that a good citizen, in my opinion, should do."

Responding to the report, US officials said Americans are only targeted for email surveillance if there is probable cause.

"Unlike some other nations, the United States does not monitor anyone's communications in order to suppress criticism or to put people at a disadvantage based on their ethnicity, race, gender, sexual orientation or religion," said a joint statement from the Justice Department and office of the Director of National Intelligence.